It is known to use control devices for knitting machines which, in order to control the length of yarn used by a knitting machine, each feeder receives yarn from a yarn feeding means which feeds yarn to it at a rate which is fixed at a value proportional to the knitting machine speed. Such yarn feeding devices commonly consist of a nip roller drive coupled to a driven part of the knitting machine and are suitable only when the required length of yarn to be knitted into each sequence of a small number of stitches is substantially constant.
When a knitting machine is fitted with needle selecting means so that the length of yarn required to be knitted into each sequence of a small number of stitches is not substantially constant the known arrangements described above are not suitable as the individual feeding devices cannot readily provide the various lengths of yarn which are required to be fed into the knitting machine at different times during the knitting. The present invention is believed to represent a solution to this problem.
According to one aspect of the present invention, there is provided a method of feeding yarn to a knitting machine having a group of yarn feeders and also having needle selecting means so that the length of yarn required to be knitted into each sequence of a small number of stitches is not constant, each individual yarn being fed to the knitting machine at an adjustable tension by one of the yarn feeders, the method including the steps of:
(1) measuring the length of an individual yarn fed to the knitting machine during each sequence of a small number of stitches;
(2) comparing the measured length to a predetermined length value which is a function of a predetermined stitch length;
(3) adjusting the tension in said individual yarn fed to the knitting machine in response to any deviation detected in comparison step (2) above; and
(4) maintaining the adjusted tension while repeating steps (1) and (2) and then repeating step (3) in response to the deviation detected during the repetition of steps (1) and (2) so as to continuously adjust the tension of said yarn fed to the knitting machine so that the actual yarn consumption in the knitting of an article is substantially equal to the predetermined yarn consumption.
Advantageously the function of said stitch length which is measured is the length of yarn being knitted.
The length of yarn being knitted can be measured in a number of ways. For example, the yarn may pass around a rotatable member and be arranged to make non-slipping contact therewith so that the length of yarn being knitted can be measured from the speed of rotation of the member. If desired, the member can be one of a pair of nip rollers.
In order to adjust the tension in the yarn fed to the knitting machine, a yarn-driven rotatable member may be employed, the tension being adjusted by controlling the resistance to rotation of the rotatable member. Again, if desired, the rotatable member may be one of a pair of nip rollers.
The tension control may be effected using a feed mechanism for the yarn which is driven by means of a tape drive. Preferably, the error detected by the comparing means is used to set a tension value and the feed mechanism is arranged to introduce the set tension into the yarn.
According to a further aspect of the present invention an apparatus for controlling the feeding of yarn to a knitting machine comprises means for measuring the stitch length of yarn which has been knitted by said machine or a function of said stitch length, means for comparing said measured stitch length or function thereof with a predetermined stitch length or comparable function thereof and means for adjusting the tension in the yarn fed to the knitting machine in response to any error detected by the comparing means.
For the purpose of carrying out the invention to control the length of yarn knitted by a knitting machine the means for determining the length of yarn LM1 being knitted by the machine may for example, be a rotating member with the circumferential surface of which the yarn makes non-slipping contact before it passes into the feeder of the knitting machine. The circumferential speed of the rotating member is thus equal to the speed of the yarn. It will be understood that the rotating member may for example conveniently be part of the adjusting means described above.
The rotation of the member as the yarn passes over it may conveniently be sensed by displacement detecting means which produces an output signal which is a measure of the length of yarn passing into the knitting machine. The displacement detecting means may conveniently be photoelectric, magnetic capacitative or pneumatic and the output signal may conveniently be in digital or analogue form and may conveniently take the form of an electrical current or voltage suitable for transmission to another location.
For the purpose of carrying out the invention to control the length of yarn being knitted by a knitting machine which has needle selecting means in operation controlled by a stored program computer, the means for producing a control signal to control the adjusting means, this control signal being related to the departure of the length of yarn knitted by the knitting machine from the required length, may be, for example, a transducer giving an output signal suitable for the control of the adjusting means in response to an electrical input signal produced by the computer. The computer may be programmed to calculate the required length to be knitted during each convenient amount of knitting displacement of the knitting machine from data supplied in the computer program. The computer may be arranged to receive the signal referred to above and to compute the departure from the required length of the length of yarn knitted by the knitting machine for each convenient amount of knitting displacement of the knitting machine and to produce the corresponding signal for the transducer which correspondingly produces the control signal for the adjusting means.
In order to control the length of yarn knitted by a knitting machine which has needle selecting means in operation controlled by electrical signals derived from a pattern data storage device, which may be for example a digitally marked film strip or a digitally encoded magnetic tape or a digitally perforated tape, the means for producing a signal to control the adjusting means is related to the departure of the length of yarn knitted by the knitting machine from the required length and may be for example a transducer giving an output signal suitable for the control of the adjusting means in response to an electrical input signal produced by for example a stored program computer provided with access to the needle selecting signals with the knitting machine. The computer may be programmed to calculate the required length of yarn to be knitted during each convenient amount of knitting displacement of the knitting machine from data supplied in the computer program. The computer may be arranged to compute the departure from the required length of the length of yarn knitted by the knitting machine for each convenient amount of knitting displacement of the knitting machine and to produce the corresponding signal for the transducer which correspondingly produces the control signal for the adjusting means.